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I've seen this short movie when I was a kid, but I don't remember the title. The story is that humans live underground, and have a lifespan of seven days.
They train a newborn on his first day and send him on a quest to open some door that will lift the curse.
On his way he battles with some monsters, plays some kind of chess with some other monster, and on the seventh day opens the door.
I remember that the short movie had animatronics, and even some CGI (this was around the late '80-ties, I think), but I can't find it anywhere.